A wireless communication system based on an Orthogonal Frequency Division Multiplexing (OFDM) can be applied to different multiple access schemes in a frequency domain and a time domain.
In the frequency domain, the wireless communication system can use the OFDM scheme in which one terminal exclusively occupies the entire frequency band in a particular time, and an Orthogonal Frequency division Multiple Access (OFDMA) scheme in which a plurality of terminals occupies different subchannels (or OFDM subchannels) in the same time.
In the time domain, the wireless communication system can use a scheduled access scheme in which a centralized scheduler manages the resource allocation of the terminals, and a random access scheme in which the terminals occupy the resources in competition.
The OFDM wireless communication system can constitute different combinations of four multiple access schemes. For example, the wireless communication system can transmit data in the first combination of the OFDM scheme and the scheduled access scheme, in the second combination of the OFDM scheme and the random access scheme, in the third combination of the OFDMA scheme and the scheduled access scheme, and in the fourth combination of the OFDMA scheme and the random access scheme. The first, second, and third combinations are adopted to Institute of Electrical and Electronics Engineers (IEEE) 802.11 and 802.16 standards.
When the wireless communication system employs the second combination, a single terminal exclusively possesses the entire frequency band in a specific time according to the OFDM scheme. Accordingly, the wireless communication system uses the random access scheme by which the terminals competitively occupy the time resource.
However, in the OFDMA scheme, the plurality of the terminals utilizes different subchannels in the same time resource. Correspondingly, in the fourth combination, the wireless communication system needs to adopt the random access scheme such that the terminals competitively occupy the resource in the two dimensional space of the time resource and the frequency resource.
Thus, what is needed is a multi-channel based random access scheme in order to transmit data using the OFDMA scheme and the random access scheme in the wireless communication system.